Particularly in large mobile loading cranes, the crane post is as a rule composed of one upper and one lower portion which are joined together to form one single unit. The lower portion serves as a pivot pin mounting the crane post to the crane base and transferring the torsional moment via a toothed gearing, from the crane rotating mechanism, which usually is in the form of a rack arranged for reciprocal displacement. The maximum allowable vehicle width limits the space available for the crane base and its rotating mechanism and in constructing the crane base portion the limited space has made it necessary to form the toothed gear ring directly in the tubular wall of the lower post portion. To meet the requirements on strength made on a cog path, high strength steel must be chosen for the lower post portion.
It is known to join the post portions by welding. However, this requires the use of a weldable steel which in the case of the gear raceway must also be temperable, and consequently tampering and heating treatments of the lower portion of the post become necessary. In addition thereto, this joining method involves problems associated with tensions arising in the material and with structural transformations of the material in the area of the weld. To avoid these problems and the coats connected therewith one wants to be free to choose a high strength steel for the lower crane post portion without having to consider the weldability thereof.
For this purpose one may apply another prior-art method of joining together the crane post portions, according to which method each crane post portion is provided with an annular outer flange by means of which the portions are secured to one another by means of bolts. The flanged bolt bond requires considerable space, however, and in addition the bond is rather heavy on account of the amount of material required therefor. In addition to the disadvantages of heaviness and requirements on space, the increased amount of material and the number of bolts required also attribute to the high costs of the flanged bond.